ASP.NET MVC 3 HtmlHelper异常无法识别继承接口上的ModelMetadata

Question

升级到MVC 3 RTM后,我得到了一个以前工作的例外.

这是场景.我有几个使用相同底层接口IActivity和IOwned的对象.

IActivity implements IOwned (another interface)

public interface IActivity:IOwned {...}

public interface IOwned 
{
    int? AuthorId {get;set;}
}

我有一个局部视图,它使用IActivity从其他具体的部分重用.

以下是Activity Partial的定义.

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<IActivity>" %>
<%: Html.HiddenFor(item => item.AuthorId) %>

但是,它会引发异常.它在ModelMetadata中找不到AuthorId.

我猜测在之前的版本中它查看了IActivity实现的接口.

任何想法,建议,到处都没有重复类似的接口？

复制下面的堆栈跟踪.

[ArgumentException: The property IActivity.AuthorId could not be found.]
   System.Web.Mvc.AssociatedMetadataProvider.GetMetadataForProperty(Func`1 modelAccessor, Type containerType, String propertyName) +498313
   System.Web.Mvc.ModelMetadata.GetMetadataFromProvider(Func`1 modelAccessor, Type modelType, String propertyName, Type containerType) +101
   System.Web.Mvc.ModelMetadata.FromLambdaExpression(Expression`1 expression, ViewDataDictionary`1 viewData) +393
   System.Web.Mvc.Html.InputExtensions.HiddenFor(HtmlHelper`1 htmlHelper, Expression`1 expression, IDictionary`2 htmlAttributes) +57
   System.Web.Mvc.Html.InputExtensions.HiddenFor(HtmlHelper`1 htmlHelper, Expression`1 expression) +51
   ASP.views_shared_activity_ascx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in c:\Users\...\Documents\Visual Studio 2010\Projects\ngen\trunk\...\Views\Shared\Activity.ascx:3
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +109
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Control.Render(HtmlTextWriter writer) +10
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +208
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Page.Render(HtmlTextWriter writer) +29
   System.Web.Mvc.ViewPage.Render(HtmlTextWriter writer) +43
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3060

Answer 1

ASP.NET MVC 3中的一个重大变化/错误在该System.Web.Mvc.ModelMetadata. FromLambdaExpression方法中解释了您获得的异常:

ASP.NET MVC 2.0:

...
case ExpressionType.MemberAccess:
{
    MemberExpression body = (MemberExpression) expression.Body;
    propertyName = (body.Member is PropertyInfo) ? body.Member.Name : null;
    containerType = body.Member.DeclaringType;
    flag = true;
    break;
}
...

ASP.NET MVC 3.0

...
case ExpressionType.MemberAccess:
{
    MemberExpression body = (MemberExpression) expression.Body;
    propertyName = (body.Member is PropertyInfo) ? body.Member.Name : null;
    containerType = body.Expression.Type;
    flag = true;
    break;
}
...

注意如何为containerType变量分配不同的值.所以在你的情况下,在ASP.NET MVC 2.0中,它的值被赋值为属性IOwned的正确声明类型,AuthorId而在ASP.NET MVC 3.0中,它被分配给IActivity以后,当框架试图找到它崩溃的属性时.

这就是原因.就决议而言,我会等待微软的一些官方声明.我在发行说明文档中找不到任何相关信息.这是一个需要在这里工作的bug或某些功能吗？

现在你可以使用非强类型的Html.Hidden("AuthorId")帮助器或指定IOwned控件的类型(我知道两个都很糟糕).

Answer 2

来自MVC团队:

不幸的是,代码实际上正在利用已修复的错误,其中用于ModelMetadata目的的表达式容器无意中设置为声明类型而不是包含类型.由于虚拟属性和验证/模型元数据的需要,必须修复此错误.

拥有基于接口的模型不是我们鼓励的(也不是,考虑到错误修复所施加的限制,可以实际支持).切换到抽象基类可以解决问题.

Answer 3

感谢Burcephal,回答的人指出了正确的方向

你可以创建一个解决这个问题的MetaDataProvider,这里的代码添加到基类中的代码中,检查模型的实现接口上的属性,该模型本身就是一个接口.

public class MyMetadataProvider
    : EmptyModelMetadataProvider {

    public override ModelMetadata GetMetadataForProperty(
        Func<object> modelAccessor, Type containerType, string propertyName) {

        if (containerType == null) {
            throw new ArgumentNullException("containerType");
        }
        if (String.IsNullOrEmpty(propertyName)) {
            throw new ArgumentException(
                "The property &apos;{0}&apos; cannot be null or empty", "propertyName");
        }

        var property = GetTypeDescriptor(containerType)
            .GetProperties().Find(propertyName, true);
        if (property == null
            && containerType.IsInterface) {
            property = (from t in containerType.GetInterfaces()
                        let p = GetTypeDescriptor(t).GetProperties()
                            .Find(propertyName, true)
                        where p != null
                        select p
                        ).FirstOrDefault();
        }

        if (property == null) {
            throw new ArgumentException(
                String.Format(
                    CultureInfo.CurrentCulture,
                    "The property {0}.{1} could not be found",
                    containerType.FullName, propertyName));
        }

        return GetMetadataForProperty(modelAccessor, containerType, property);
    }
}

如上所述,将您的提供程序设置为global.asax Application_Start

ModelMetadataProviders.Current = new MyMetaDataProvider();

Answer 4

如果您有兴趣,我已经在我的应用程序中实现了一些工作.当我浏览MVC源代码时,我发现下面命名的FromLambdaExpression方法将调用MetaDataProvider,它是一个可覆盖的单例.所以我们可以实现那个实际尝试固有接口的类,如果第一个不起作用的话.它也将上升到接口树.

public class MyMetaDataProvider : EmptyModelMetadataProvider
{
    public override ModelMetadata GetMetadataForProperty(Func<object> modelAccessor, Type containerType, string propertyName)
    {
        try
        {
            return base.GetMetadataForProperty(modelAccessor, containerType, propertyName);
        }
         catch(Exception ex)
        {
            //Try to go up to type tree
            var types = containerType.GetInterfaces();              
            foreach (var container in types)
            {
                if (container.GetProperty(propertyName) != null)
                {
                    try
                    {
                        return GetMetadataForProperty(modelAccessor, container, propertyName);
                    }
                    catch
                    {
                        //This interface did not work
                    }
                }
            }               
            //If nothing works, then throw the exception
            throw ex;
        }              
    }
}

然后,只需在global.asax Application_Start()中实现MetaDataProvider的实现

ModelMetadataProviders.Current = new MyMetaDataProvider();

它不是有史以来最好的代码,但它完成了这项工作.

Answer 5

尝试使用类型转换。它适用于我的项目，尽管 resharper 强调它是多余的。

对于您的代码，解决方案是

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<IActivity>" %>
<%: Html.HiddenFor(item => ((IOwned)item).AuthorId) %>